Identification of the sigB Operon in Staphylococcus epidermidis: Construction and Characterization of a sigB Deletion Mutant

The role of the alternative sigma factor ς(B) in Staphylococcus epidermidis was investigated by the construction, complementation, and characterization of a sigB deletion mutant. Electrophoretic analyses confirmed a profound influence of ς(B) on the expression of exoproteins and cytoplasmic proteins. Detailed investigation revealed reduced lipase and enhanced protease activity in the ς(B) mutant. Furthermore, no significant influence of ς(B) on heterologous biofilm formation or on the activity of the global regulator agr was detected

ς(B) Activity Depends on RsbU in Staphylococcus aureus

Derivatives of the widely used laboratory strain Staphylococcus aureus NCTC8325, which are natural rsbU mutants, were shown to be unable to produce RsbU, a positive regulator of the alternative sigma factor ς(B). The lack of RsbU prevented the heat-dependent production of ς(B)-controlled transcripts and resulted in reduced H(2)O(2) and UV tolerance, enhanced alpha-hemolysin activity, and the inability to produce the alkaline shock protein Asp23. After 48 h of growth, rsbU mutant strains failed to accumulate staphyloxanthin, the major stationary-phase carotenoid. Transcription of Asp23 was found to be exclusively controlled by ς(B), making it an excellent target for the study of ς(B) activity in S. aureus. Reporter gene experiments, using the firefly luciferase gene (luc+) fused to the ς(B)-dependent promoter(s) of asp23, revealed that ς(B) is almost inactive in 8325 derivatives. cis complementation of the 8325 derivative BB255 with the wild-type rsbU gene from strain COL produced the rsbU(+) derivative GP268, a strain possessing a ς(B) activity profile comparable to that of the rsbU(+) wild-type strain Newman. In GP268, the heat inducibility of ς(B)-dependent genes, Asp23 production, alpha-hemolysin activity, pigmentation, and susceptibility to H(2)O(2) were restored to the levels observed in strain Newman, clearly demonstrating that RsbU is needed for activation of ς(B) in S. aureus

The LacI/GalR family transcriptional regulator UriR negatively controls uridine utilization of Corynebacterium glutamicum by binding to catabolite-responsive element (cre)-like sequences

Brinkrolf K, Ploeger S, Solle S, et al. The LacI/GalR family transcriptional regulator UriR negatively controls uridine utilization of Corynebacterium glutamicum by binding to catabolite-responsive element (cre)-like sequences. MICROBIOLOGY. 2008;154(4):1068-1081.The Cg1547 protein of Corynebacterium glutamicum ATCC 13032 is a member of the LacI/GalR family of DNA-binding transcriptional regulators. A defined deletion in the cg1547 gene, now designated uriR (uridine utilization regulator), resulted in the mutant strain C. glutamicum KB1547. Comparison of gene expression levels in C. glutamicum KB1547 and the wild-type strain revealed enhanced expression of the uriR operon genes cg1546 (ribokinase), cg1545 (uridine transporter) and cg1543 (uridine-pref erring nucleoside hydrolase). Gene expression of the uriR operon was stimulated by the presence of either uridine or ribose. Growth assays with C. glutamicum mutants showed that functional Cg 1543 and Cg 1545 proteins are essential for the utilization of uridine as the sole carbon source. Transcriptional regulation of the uriR operon is mediated by a 29 bp palindromic sequence composed of two catabolite-responsive element (cre)-like sequences and located in between the mapped -10 promoter region and the start codon of uriR. A similar cre sequence was detected in the upstream region of rbsK2 (cg2554), coding for a second ribokinase in C. glutamicum ATCC 13032. DNA band-shift assays with a streptavidin-tagged UriR protein and labelled oligonucleotides including the cre-like sequences of uriR and rbsK2 demonstrated the specific binding of the purified regulator in vitro. Whole-genome DNA microarray hybridizations comparing the gene expression in C. glutamicum KB1547 with that of the wild-type strain revealed that UriR is a pathway-specific repressor of genes involved in uridine utilization in C. glutamicum

Biomimetic synthesis and structural reassignment of the tridachiahydropyrones

The biomimetic synthesis and structural reassignment of tridachiahydropyrone, tridachiahydropyrone B and tridachiahydropyrone C, isolated from mollusks of the order Sacoglossa, using a sequenceof photochemical transformations from a common polyene precursor are described. These complex naturalproducts may act as sunscreens for the producing organism, thus offering protection from harmful UV radiation and oxidative damag